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Subject[PATCH 2/2] Implement simple hierarchical draining
Date
From: Andi Kleen <ak@linux.intel.com>

Instead of draining all CPUs immediately try the neighbors first.
Currently this is core, socket, all

Global draining is a quite expensive operation on a larger system,
and it does suffer from quite high lock contention because all
CPUs bang on the same zones.

This gives a moderate speedup on a drain intensive workload,
and significantly lowers spinlock contention.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
mm/page_alloc.c | 38 ++++++++++++++++++++++++++++++++++----
1 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8cd4f6a..d7dea3f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1196,6 +1196,36 @@ void drain_all_pages(void)
on_each_cpu(drain_local_pages, NULL, 1);
}

+enum {
+ DRAIN_CORE,
+ DRAIN_SOCKET,
+ DRAIN_ALL,
+ /* Could do nearby nodes here? */
+ NUM_DRAIN_LEVELS,
+};
+
+/*
+ * Drain nearby CPUs, reaching out the farther the higher level is.
+ */
+static void drain_all_pages_level(int level)
+{
+ const cpumask_t *mask;
+ int cpu = smp_processor_id();
+
+ switch (level) {
+ case DRAIN_CORE:
+ mask = topology_thread_cpumask(cpu);
+ break;
+ case DRAIN_SOCKET:
+ mask = topology_core_cpumask(cpu);
+ break;
+ case DRAIN_ALL:
+ mask = cpu_online_mask;
+ break;
+ }
+ smp_call_function_many(mask, drain_local_pages, NULL, 1);
+}
+
#ifdef CONFIG_HIBERNATION

void mark_free_pages(struct zone *zone)
@@ -2085,7 +2115,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
{
struct page *page = NULL;
struct reclaim_state reclaim_state;
- bool drained = false;
+ int drained = 0;

cond_resched();

@@ -2121,9 +2151,9 @@ retry:
* If an allocation failed after direct reclaim, it could be because
* pages are pinned on the per-cpu lists. Drain them and try again
*/
- if (!page && !drained) {
- drain_all_pages();
- drained = true;
+ if (!page && drained < NUM_DRAIN_LEVELS) {
+ drain_all_pages_level(drained);
+ drained++;
goto retry;
}

--
1.7.7.6


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